Electrical network



1,638,437 1 D. K.'GANNETT E AL ELECTRICAL NETWORK Filed April 27. 1920 g g g 1 INVENTORS I l v I E 5? ATTORNEY Patented Aug. 9, 1927.

UNITED STATES PATENT OFFICE.

DANFORTH K. GANNETT, OF ARVERNE, NEW YORK, AND MACLEAN KIRKWOOD,

EAST ORANGE, NEW JERSEY, ASSIGNORS TO AMERICAN TELEPHONE AND TELE- GRAPH COMPANY, A CORPORATION OF NEW YORK.

ELECTRICAL NETWORK.

Application filed April 27, 1920. Serial No. 376,996.

This invention relates to electrical net-' works, and especially to a type of aperiodic network which is adapted to modify the voltage wave impressed thereon in such mannor that the wave at the output end of the said network closely approximates in form any desired integral or derivative of the impressed wave depending upon the type of network used.

Networks heretofore devised for approximating a required integral or derivative of an impressed voltage wavemay be rendered free from undesirable interaction between the component parts only by the insertion of some form of unilateral device at suitable points, or by'proportioning the constants of the successive networks so that the current transmitted therethrough becomes unduly diminished, or by greatly increasing the impedanceof the circuits.

"it is the object of the present invention to provide networks involving resistances, inductances and capacities combined so as to closely approximate any required integral or 25 derivative of an impressed wave, which networks require no unilateral devices to prevent interaction between the parts and do not cause undue diminution of the transmitted current, or other undesirable results.

The integrating or differentiating networks of' this invention are of the nature of low pass and high pass filters respectively.

The integrating networks simulate the low pass type, being designed to transmit with slight attenuation a range of low frequencies and to attenuate greatly the frequencies above a certain critical frequency. In a converse manner, the differentiating networks transmit readily the upper range or band of frequencies and subject the lower fre uencies to greater attenuation. It will he s own later that the integrating networks produce a wave that closely approximates a true integral of the impressed wave throughout the frequency ran e above the aforesaid critical frequency, and similarly the different-iating network approximates a true derivative of the impressed wave through the frequency range below the critical frequency, the said critical frequency depending on the time-constant of the circuit.

Such networks, especially of the integrating type, are found advantageous in submarine cable .telegraphy, in order to screen the receiving apparatus of such cables from the effects of transient interference waves set up in. said cable, and the same time to freely transmit the signaling waves received over thesaid cable. This invention has accordingly been described in its relation to such type of telegraphy, but it is to be, understood, however, that it is not so limited, but may be used in any type of circuit where it is desired to obtain an integral or derivative of a variable voltage wave.

-This invention will be better understood from the following description when read in connection with the attached drawing, of which Fig, 1 shows the arrangement of the network for four successive integrations of an impressed voltage wave; Fig. 2 shows in detail one unit illustrating the basic principles involved; Fig. 2 shows the first step n building up a network comprising more than one unit; Fig. 3 shows a method for combining theseunits in a network producing the fourth integral of the impressed wave; Fig. 4 shows graphically the first, third and fourth integrals, and Fig. 5 shows the arrangement of the elements to obtain, for example, the fourth derivative of an impressed variable voltage wave.

In Fig. 1, 1 represents a transmission line having large distortion and attenuation characteristics such as a submarine telegraph cable, which is connected to a winding 12 of the transformer 5, the other side of said winding being connected to an artificial line 2, adapted to balance the submarine cable. A transmitting device 3' which may be of any well known type is connected to the midpoint of winding 12. Bridged across the other winding 4 of the transformer 5 is an interference reduction network comprising four sub-networks 6, 7 8 and 9, each of the said sub-networks comprising an inductance L in series with the line, a resistance R and a capacity C in series with the said resistance bridged across the line. Network 9 terminates in resistance R the value of which may be determined by equations hereinafter set forth. Across R, is bridged the in ut side of a vacuum tube amplifier 10, whic is adapted to impress the amplified wave upon a. recording device 11. would be obtained by bridging the input sidev of the amplifier across the condenser C, in the manner shown in Fig. 1.

The same result:

Fig. 2, as stated, shows a single unit em- .Bridged across the last network is a resistbodying the basic principles of this invenance R. the value-of which may be detertion, comprising two parallel circuits, one of mined by equations hereinafter set forth. which has in series a resistance R and a The network of Fig. 5 may be derived by capacity 0,, and the other of which has in extending the fundamental network shown series a resistance R equal to the resistance in Fig. 2 by a process of substitution, in'

R, and in series therewith an inductance L general, similar to the method of developing It will be shown later that the impedance the integrating networks shown in Figs. 2, of such circuit when its constants are prop 2 and 3, but differing therefrom in that erly proportioned is equal to the resistance each additional network replaces the resistin either branch at all frequencies. Accordance in the capacity branch instead of the ingly, there may be substituted for the reresistance in the inductance branch of the sistance R, another network similar to that preceding network. Each of these sub-netshown in Fig. 2, whicharrangement is illusworks produces a voltage wave which is the trated clearly inFig. 2. derivative of the wave impressed thereon.

Fig. 3-shows means for combining a plu- It will be seen, therefore, that any desired rality of sub-networks as shown in Fig. 2 so derivative may be obtained by connecting as to obtain, for example, at the output side together in the manner shown, a number of of the said network the fourth integral of sub-networks corresponding to the desired the impressed voltage wave. It will be seen derivative. The same result may be obtained that the network shown in Fig. 1 in connecby an inductive coupling shown in Fig. 5

tion with the terminal circuit of a submarine across the inductance L, since the voltagecable telegraph system is only a re-arrangewave across L is the same as that across ment of the circuit shown in Fig. 3. I the resistance R Fig.4 shows graphically the relation be- Having in mind the foregoing description tween the ratio of the output voltage to the of the circuits and the functions of the cominput voltage of the network and the freponent parts, this invention will be more quency, whena network such as is shown in clearly understood from the following de- Figs. 1 and 3 is inserted in the circuit. The scription of the manner in which the circuit curves a, b, and 0 represent respectively the operates when an impressed variable voltage first, third and fourth inte rals of the imwave, such as a transient interference wave pressed voltage wave. It wlll be noted that is impressed across the winding 4 of the the curves fall off sharply after passing a transformer 5. certain frequency value, Since the interfe Consider first the unit network shown in ence a es are of e atl e y hig equency Fig. 2. If the two resistances therein repreoompared with the signaling waves, they will be reduced in magnitude whereas the signaling frequency will pass through the network substantially unaffected thereby.

Fi 5 Shows th arrangement f th tand the lnductance L is assumed to have zero work to obtain for example, the fourth dereslstfimc'e, the Retwofk as Shown 111 the figrivative of an impressedyoltage Wave. It ure Wlll have an impedance equal to the res stcomprises four sub-networks, each of which time R R' for all frequencies of the 1mis made up of a capacity C in series with the pressed wave. This W111 be seen from the folline and a resistance R in series with an inlowing derivation of the impedance of the ductance l3, connected across the line. circuit:

1 1 (Rd-1001A) +(R+ 2R+y(wL- Since, therefore, the impedance of the circuit represented in Fig. 2 is equivalent to v the VB R, we may substitute such a circuit for the resistance R in the manner shown in Fig. 2*. In this figure, the elements B C and L are the same as the similarly designated parts of Fig. 2, but in place of the resistance R we have substituted a circuit of equivalent impedance comprising a resistance R a capacity C an inductance L and a resistance B. This process may be carried further by substituting for R a third network, and by thus adding to the basic network the required number of sub-networks,

in which R R R w 2% X frequency and L 1 ='1/- 1. If R E3 E equation by substitution becomes R +R "(RwL- 5 Z L 2 a [2R+i wL- Z R sented by R and R are each equal to Assuming a voltage E impressed acrossthe network, the voltage drop 6 across the resistance R in terms of the impressed voltage is If the frequency is above a certain critical value, the voltage drop across the inductance L is substantially .E, and consequently the current through L, is related to the voltage E substantially in accordance with the following equation:

which, when rearranged in form, is

If we multiply the preceding equation by It will be seen that equation 1 approaches in ian.

value equation .2 for those frequencies at which the voltage drop across the inductance L is substantially equal to E, because at those frequencies jwL, becomes large relative to R. Therefore, the network as shown in Fig. 2 may be said to approximately integrate the impressed voltage wave for frequencies above the critical frequency, and the approximation to an exact integral being proportional to the distance from the critical frequency.

In a similar'manner, it may be shown that for frequencies below a limiting value, such that the impedance of the condenser C, is great compared with its resistance R,, the current through the condenser and hence the voltage across the resistance approximates the first derivative of the voltage E. The limiting value of frequency below which this approximation approaches the actual condition is proportional to the reciprocal of the time constant of C, and R, and therefore may be made any required value.

Since, however, it is impracticable to obtain inductance coils having zero resistance, the values of the elements of the networks must be modified in order to apply this principle to a practical case. If R represents the resistance of one inductance coil,

the conditions which must be satisfied are that R .H/ -R IT. R

in which the subscripts denote the number of the section of the network under consideration. Thus in the sub-network 7 the value of the resistance is Also, since R differs from R, we must and change the values of L 01" C, so that The value of the resistance R may be determined from the foregoing equations in the same manner in which the magnitude of the other resistance elements is obtained.

By means of the arrangements represented in Figs. 1 and 3, having inductances in series with a source of variable voltage waves and capacities with resistances in series bridged across the said source, the integral of the impressed wave corresponding to the number of sections of network may be obtained. That is to say, with a network having four sections, the impedance of which is equal to R at all frequencies, the voltage E impressed across the input circuit of the amplifier 10 is represented by the equation The result of the successives integrations is clearly shown by curves a, b, and 0 in Fig. 4;, in which theprdinates represent the ratio of the output voltage E to the input voltage E, across said network and the abscissae represent frequency. It will be noted that the voltage values are greatly reduced beyond a certain critical frequencya-nd that successive integrations tend to diminish the magnitude of the voltage values. Since transient interference waves in submarine cables have relatively higher frequencies than the impremed signaling waves, the amplitude of the signaling voltage is relatively unaffected by such a network as is shown in Fig. 1,. provided the frequency of the signaling wave is kept below the critical frequency indicated by as upon the curves of Fig. 4. It Will,'therefqre, be seen that this network tends to screen the receiving apparatus from the effects of a high frequency transient wave, and at the same time, to readily transmit to the said apparatus, the lower frequency signaling wave. work, furthermore, does not require the insertion of a unilateral device between the.

This net- I said source.

component sub-networks since there is no interaction between the various parts.

Any desired derivative of an impressed variable voltage, E may be obtained by .a network of the required number of sections such as that shown in Fig. 5, in which the capacities are in series with the source of impressed voltage waves, and the inductances in series with resistances are bridged across the With such an arrangementof the elements, the networks shown in Fig. will be adapted to produce a voltage wave E, representing the derivative of the impressed voltage wave E The value of the terminating resistance R may be obtained in the same manner in which the value of the other resistances is obtained, viz, from the formula Where R, is any resistance, R is the value of the resistance of the preceding sub-network and R is the resistance of the inductance coils such as L, L", etc. The relation between the voltages E, and E, may be represented by the equation It will be seen that by grouping together any desired number of unit networks having elements of the proper values, any desired integral or derivative of a variable voltage wave may be obtained. Furthermore, such network or group of networks furnish an interference reduction device which requires the use of no unilateral device between the component unit networks to prevent interaction therebetween. This network, as has been shown, does not appreciably affect the magnitude of the signaling voltage waves provided the frequency there-,

of is kept within certain limits. Also, since the impedance of thearrangement is equiva-- lent to pure resistance, at all frequencies, such network may be correctly terminated by a resistance element.

Although this invention has been disclosed as embodied in a particular form, it

' is to be understood that it is not so limited assess? said elements being so proportioned that the impedance of the said network is equal to the resistance at all frequencies.

2. In an electrical circuit, the combination of a source of variable voltage waves, an aperiodic network adapted to be connected with the said source, a receiving apparatus adapted to be connected with the network, said network comprising a resistance in series with a capacity bridged across said source, an inductance in series with said source, and a second resistance bridged across the input side of the said receiving apparatus, the values of the elements being so proportioned that the impedance of the circuit at all frequencies is substantially pure resistance, whereby the integral of the impressed voltage wave may be impresed on the said receiving apparatus.

In an electrical circuit, the combination of a source of a variable voltage wave, of a network substantially aperiodic, and a receiving circuit connected therewith, the said network comprising a resistance and a capacity serially bridged across said source, an inductance in series therewith, and a second resistance bridged across the input side of the said receiving circuit, the elements being so proportioned as to produce a wave form which is substantially the integral of the impressed Wave, and to impress said integral upon the receiving circuit.

4. In an electrical circuit, the combination with a source of a variable voltage wave, of an aperiodic network comprising a plurality of sub-networks each including a resistance and a capacity serially bridged across said source, an inductance in series with said source, and a resistance bridged across the last sub-network, the values of the elements in each of said sub-networks being so proportioned that the impedance of the said network is substantiaily pure resistance, and a receiving circuit adapted to receive the voltage wave impressed by said network.

5. In a signaling system, the combination with a transmission circuit of a terminal circuit comprising an aperiodic network made up of an inductance in series with said circuit, a'resistance in series with a capacity bridged across said circuit, a receiving apparatus, the said network being'so designed as to attenuate transient interference waves arriving over said transmission circuit, and to pass substantially unaffected the lower frequency signaling waves.

6. In an electrical signaling system, the combination with a transmission circuit of a terminal circuit comprising an aperiodic network made up of a group of sub-networks, each including an inductance in series with the circuit and a resistance in series with a capacity bridge across the cir cuit, the sub-networks being so related that the respective inductances are in series and the respective resistances and capacity branches will be bridged in parallel across said terminal circuit, whereby the desired integral of any impressed transient wave may be obtained.

7. An electrical filter having a single cut ofi point comprising a plurality of a riodic networks, each having a series mem er consisting of reactance and a shunt member consisting of resistance in series with reactance.

8. An electrical filter having a single cutoff point comprising a plurality of aperiodic networks, each having a series member consisting of reactance and a shunt member consisting of resistance in series with reactance, the reactance in said shunt member being of 0 p'osite phase angle to the reactance in sai series member.

In testimony whereof we have si ed our names to this specification this 261: day of April 1920.

DANFORTH K. GANNETT. MACLEAN KIRKWOOD. 

